Webley CO2 output valve o-rings?

[SSPKali]

Hi,

I am trying to sort a leaking output valve on a friends Webley CO2 pistol (might be a Well?) and despite greasing the orings and threads and doing the valve up tight it is still leaking when a bulb is fitted.

Are o-rings for CO2 different to green gas use? Possibly due to higher pressure and lower temperature. Any ideas on sizes, if anyone has done this before?

 

[SSPKali]

10mm ID X 1mm thick for big one on the brass part.

4mm ID x 1.5mm thick for the front one.

You’re welcome ?